As exemplified by carbon fiber reinforced plastic (CFRP) and glass fiber reinforced plastics (GFRP), the composite material in which a resin and fiber are combined is widely used in various industrial fields such as aircraft.
In a member formed of composite material (to be referred merely to as “a composite material member” below), a defect often occurs. Especially, when mechanical processing (e.g. drilling) is carried out to the composite material member, a defect caused by damage due to the mechanical processing sometimes occurs. To confirm the existence or non-existence of such a defect, an inspection is carried out in a manufacturing process and a processing process of the composite material member.
The most typical inspection method of the composite material member is an ultrasonic inspection. In the ultrasonic inspection, ultrasonic wave is incident to the composite material member and the reflection wave returned from the composite material member is acquired. The position and size of a defect can be detected from information contained in this reflection wave.
However, when a plurality of defects are arranged in the incidence direction of the ultrasonic wave, there is a case which is insufficient to the detection of a defect by the ultrasonic inspection. When the plurality of defects are arranged in the incidence direction of the ultrasonic wave, the ultrasonic wave is reflected by the defect which is the nearest to the incident position of the ultrasonic wave. In such a case, only the defect which is the nearest to the incident position can be detected in the ultrasonic inspection, and the detection miss of the defect can occur. Especially, an interlayer delamination occurs when mechanical processing is carried out to the composite material member in which sheets or cloths formed of fiber are stacked, and the interlayer delamination is easy to generate in a specific direction (for example, a direction in which the fiber sheets and the fiber cloths are stacked) so that it is easy for an inspection error of the defect to occur.
Note that the ultrasonic inspection of a though-hole formed in the composite material is disclosed in US 2012/0035862 A1.